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Insect to be released to combat invasive weeds in Southwest Colorado

Knapweed harms native plants, animals

The Bureau of Reclamation announced Thursday it will partner with other agencies to release an insect at two Southwest Colorado wetlands to combat the invasive Russian knapweed.

Durango Herald file

Insect to be released to combat invasive weeds in Southwest Colorado

The Bureau of Reclamation announced Thursday it will partner with other agencies to release an insect at two Southwest Colorado wetlands to combat the invasive Russian knapweed.

Durango Herald file

A wasp will be brought to two Southwest Colorado wetlands this spring to join the battle against the noxious Russian knapweed, which harms native plants and wildlife.

The effort, according to the Bureau of Reclamation, will target the aggressive, non-native plant that, if left unmanaged, displaces native plant species and can cause neurological disorders in some animals, including horses, that eat it.

According to Colorado state data, Russian knapweed originates near the Caspian Sea in western Asia but was introduced to the U.S. in the late 1880s with alfalfa seeds. It is now found in most of the U.S. west of the Appalachian Mountains but is most problematic in semi-arid rangelands of the West.

Russian knapweed has no agricultural or ecological value, the state’s Department of Agriculture said, and it out-competes crops, degrades rangeland and takes over habitats.

For years, the state of Colorado has battled the spread of Russian knapweed, using gall midges from an insectary in Palisade. The insect, which can eat away at the weed, has been used since 2009.

In a news release Thursday, the Bureau of Reclamation said it would partner with Colorado Parks and Wildlife and the Palisade Insectary to attack the plant with another insect, the stem gall wasp, in an “innovative and environmentally conscious” way this spring.

The project will focus on wetlands on the Colorado side of Navajo State Park and Simon Draw Wildlife Area in Montezuma County.

The gall wasp, according to the Bureau of Reclamation, causes the formation of galls or abnormal growths along the stem of the Russian knapweed, cutting off nutrients to other parts of the plant. As a result, the weed’s ability to grow and spread is significantly hampered.

Justyn Liff, spokeswoman for the Bureau of Reclamation, said gall wasps have been used in other areas.

“It’s been used before and been successful in keeping the knapweed from thriving,” she said. “And it’s something different than going in and using weed spray or hand pulling.”

The gall wasps require little management after they are released, the Bureau of Reclamation said, and move around through flight, wind or on wildlife. The insects do not affect humans, livestock or other plant species.

In just three growing seasons, the Bureau of Reclamation said every Russian knapweed stem at the research site in Palisade was affected, and the overall health of the patch was diminished.

“Impacts from the gall wasp can be seen relatively rapidly as evidenced by trials at other sites conducted by the Palisade Insectary,” the Bureau of Reclamation said in the release.

Liff said the Bureau of Reclamation does not have a specific start date for the project.